Select how the image is acquired, then enter the geometry settings that directly determine voxel dimensions.
2D Slices
3D Volume
2D acquisition
Acquires separate physical slices. In-plane pixels can be very small, while slice thickness is often larger, producing anisotropic voxels. It is often less sensitive to motion affecting the entire volume.
Geometry
Frequency FOV (mm)
Controls coverage in the readout direction. A larger FOV with the same matrix creates a larger pixel with more signal but less spatial detail.
Frequency Matrix
More frequency samples create smaller pixels and finer detail, but each voxel contains less signal.
Phase FOV (mm)
Controls coverage in the phase direction. Reducing it makes phase pixels smaller, but anatomy outside the FOV may wrap into the image.
Phase Matrix
More phase steps improve phase-direction detail and make voxels smaller, but can reduce SNR and increase scan time.
Slice Thickness (mm)
Directly sets the third voxel dimension. Thinner slices improve through-plane detail and reduce partial volume averaging, but collect less signal.
Results
Frequency Pixel: 1.25 mm
Phase Pixel: 1.43 mm
Voxel Volume: 7.14 mm³
Slice thickness: 4.00 mm
Voxel Size Guide
Current: 1.25 × 1.43 × 4.00 mm
Anisotropic
The largest dimension is 3.2× the smallest. Detail will be lower along the thickest direction.
Smaller voxel
More spatial detail and less partial-volume averaging, but lower SNR and potentially longer scans.
Larger voxel
More signal and often faster acquisition, but less detail and more tissue averaging within each voxel.
To make the voxel smaller
• Reduce FOV while keeping matrix unchanged.
• Increase frequency or phase matrix while keeping FOV unchanged.
• Reduce slice thickness.
There is no universally best voxel size. Choose the smallest voxel that still provides adequate SNR, coverage, and scan time for the anatomy and clinical question.
Why Voxels Matter
Partial-volume effect
A voxel reports the combined signal of everything inside it. A small abnormality may remain distinct in a small voxel but become averaged with surrounding tissue inside a larger voxel.
Small voxels
Lesion stays distinct
Large voxel
Signal is averaged
Small-lesion visibility
Smaller voxels can show finer boundaries and small lesions that may be blurred or missed when the voxel approaches the size of the finding.
Multiplanar reformats
Isotropic voxels provide similar detail in axial, sagittal, and coronal views. Thick anisotropic voxels make reformatted planes look softer in the thick direction.
Current voxel: Anisotropic. Reformats will have less detail along the thickest dimension.
SNR versus detail
Smaller voxels collect signal from less tissue, so images can look noisier. Larger voxels collect more signal, but sacrifice spatial detail.
Measurements and segmentation
Smaller, well-shaped voxels can define tissue boundaries more precisely and reduce errors when measuring or segmenting small structures.
Scan time and motion
Higher-resolution imaging often needs more encoding steps or averages to recover SNR. Longer acquisitions provide more time for patient motion to blur or ghost the image.
Voxel size is one part of image quality. Contrast, coil, field strength, acceleration, motion, and reconstruction also matter.